watch一次、深度watch、访问dom更新后的`eleRef`

/**
 * 挑战 1: Watch 一次
 * 确保副作用函数只执行一次
*/
const unWatch = watch(count, () => {
  console.log("Only triggered once")
  unWatch()
})

/**
 * 挑战 2: Watch 对象
 * 确保副作用函数被正确触发
*/
const state = ref({
  count: 0,
})
watch(state, () => {
  console.log("The state.count updated")
}, {
  deep: true
})
state.value.count = 2



/**
 * 挑战 3: 副作用函数刷新时机
 * 确保正确访问到更新后的`eleRef`值
*/
const eleRef = ref()
const age = ref(2)
watch(age, () => {
  console.log(eleRef.value)
}, {
  flush: 'post'  // 'pre' | 'post' | 'sync'    default: 'pre'
})
age.value = 18 

<template>
    <p ref="eleRef">
      {{ age }}
    </p>
</template>